Installed SSL cert through cPanel for site. Edited .htaccess, everything worked great. Two weeks later, for some reason we set in Joomla Global Configuration .../Server Settings/Server/Force HTTPS to "Entire Site" (was at "None"). Got warning 'server not support ssl...'. Then visits to homepage show 404 error.

Turned off Force HTTPS back to "None". Problem continues.
All other pages/urls on site can be viewed no problem, only /index.php gives 404 error.
Advice Thank You.

Thank you. Could have been .htaccess, or configuration.php.... Anyway rather than dig around, we did a restore (Akeeba) from a 2 day old backup. Once again now entire site shows correct SSL urls.

Going forward will no longer use the "Force HTTPS" option in Joomla panel, but will use .htaccess to force https. Can not say at this point if the Joomla option was the bad, but everyone, Backup, Backup often. Then backup.